The white cane is commonly used by the visually impaired as a tool for navigation while on foot. The purpose of the cane is two-fold. First, by moving the cane in a sweeping motion back and forth across the ground, the user gains information about possible obstructions in their path. Second, the white color of the cane alerts fellow pedestrians and motorists to the presence of the user. In addition to a long cane shaft, white canes usually have a handle at one end for gripping the cane and a tip at the other end. A variety of different tip shapes are available.
Electronic travel aids (ETAs) are electronic devices for alerting a user of objects or obstacles in their path as they move through an environment. ETAs are of particular importance in improving the mobility of the visually impaired and are often mounted on white canes. The ETA first detects objects within its detection area and then communicates this information to the user through a haptic interface or some other non-visual form of communication. A haptic interface relays this information by producing tactile feedback, such as vibrations.
Early work on using optical measurement devices as ETAs has been published by J. Malverin Benjamin in “The Laser Cane”, Bulletin of Prosthetics Research, pp. 443-450, 1974. The work proposed the use of three laser beams to monitor the downward, forward and upward direction by laser triangulation method. The ETA warns the user with acoustic signals and by actuating a stimulator in contact with the index finger when dropoffs appear in front of the user (downward stairs, edges of station platforms, open manholes, etc.) and when any obstacles appear within a selectable distance range.
In “A Context-Aware Locomotion Assistance Device for the Blind”, People and Computers XVIII—Design for Life, September, 2004, pp. 315-328, Springer-Verlag, Christophe Jacquet et al. presented an ETA with an optical detection system. The first device generation named “Tom Pouce” is an infrared proximeter based on several LEDs with collimated beams in different directions and different emission powers. An obstacle in the covered field of view generates back scattered light and, if the photoelectric signal is above a fixed threshold, the device vibrates to alert the blind. Whereas this simplified first generation device is for beginner users, the more advanced second generation device, named “Teletact”, is a handheld laser telemeter with two user interfaces: a tactile and a sonorous one. The tactile interface has two vibrating elements for two fingers for a distance of up to 6 meters. The sonorous interface is for a distance of up to 15 meters and the distance information is coded in 28 different musical notes so that during scanning the obstacle profile is relayed as a melody. The obstacle distance is determined by the laser beam spot size on the object measured with a CCD image sensor line. For this advanced device, a 6 month training course is intended, as reported by Rene Facry et al. in “Laser Telemetry to improve the mobility of blind people: report of the 6 month training course”, http://www.lac.u-psud.fr/teletact/publications/rep_tra—2003.pdf. The “Tom Pouce” device tries to estimate depth simply by looking at the reflected intensity, whereas the “Teletact” device actually measures the distance by triangulation.
The Laser Long Cane device commercialized by Vistac GmbH, Germany (http://www.vistac.com/) is an ETA in a white cane for detecting obstacles at trunk and head level in front of a user, which are not detected by the conventional long cane. It is based on an infrared laser ranging detection system that measures the object distance. The laser beam faces forward and upward in direction and the distance range is adjustable in a range of 120 up to 160 cm. If an obstacle in this range at trunk or head level appears in front of the user, a vibration of the entire cane handle is generated.
Several state-of-the-art commercial handheld ETAs are based on ultrasonic detection systems. Examples include Ultracane from Sound Foresight Technology Limited, UK (http://www.ultracane.com/) and Ray from CareTec, Austria, with acoustic and haptic interfaces for alerting the user when obstacles in a range of 1.5 m up to 3 m are detected.
A device for guiding the blind is described by Sebastian Ritzler in the German patent application DE 10 2006 024 340 B4. The device has an ultrasonic sensor or a camera detection system integrated in the handle of a white cane and at the cane's tip is a power driven wheel for guiding the user around obstacles. The wheel is power driven only in the case of an unobstructed path. The device guides the user with the driven wheel but does not to give feedback on his surroundings therefore removing the original functionality of the white cane.
A further idea for a handheld ETA with a camera or 3D sensor detection system and a haptic interface is described by T. Leberer, Scylab GmbH in the patent application DE 10 2004 032 079 A1. The haptic interface consists of one or several lines of movable tracer pins, which are electronically actuated for transferring the image data to the user.
In his thesis work “Next generation of white cane”, Simon Gallo presented at EPFL 2009-10 (Simon Gallo, Next generation white cane, Master Thesis, Ecole Polytechnique Fédérale de Lausanne, January 2010) a white cane with different types of sensors and haptic feedback (vibrotactile and mechanical shocks). Specifically as range sensors, he mentions ultrasonic sensors, triangulation sensors and single point time-of-flight laser sensors.